A measurement instrument based on reflection-supported pyrometric interferometry (RSPI) has demonstrated a capability for concurrent, real-time, in situ measurement of film thickness and temperature. Resolution of thickness and temperature is 1 nm and 0.5 deg C, respectively, and under certain conditions, both may be increased by a factor of 10. The measurement system as been used to monitor rapid thermal processing (RTP), molecular beam epitaxy, and standard silicon process. This capability could faciliatate control of most semiconductor processes in which temperature and film thickness play a dominant role. The Pyritte-RS instrument can be retrofitted to single-wafer tools to provide a cost-effective solution for increasing process reproducibility and enhancing yield.